# Physics

What is the speed of a proton whose kinetic energy is 12.9 keV?

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1. Kinetic energy is 1/2 m v^2

1 eV = 1.6 * 10^-19 Joule so
12.9 keV = 2.0668 * 10^-15 Joule
mass of proton = 1.67 * 10^-27 kg
substituting

v^2 = 2 * 2.0668 * 10^-15/(1.67 * 10^-27)
v^2 = 2.475 * 10^12
v = sqrt(2.475 * 10^12)
v = 1.57 * 10^6 m/sec

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